they should be good. As a matter of fact, you should be able to claim both. The guy who built something will simply have to remove it. Too bad. He is the one that built on a recorded right of way.

the other guy may give you problems as well since many folks do not like traffic across a septic system. He too, is in the wrong.

I would make the purchase contingent upon the correction and clearance of the ROW. If you wait until after, you will have to pay for the fight. If part of the deal, the sellers will have to pay for it.